Regulation of Gene Expression Flashcards
What is a Gene?
A segment of DNA which codes for a single polypeptide (protein)
What is a Polycistrionic mRNA?
A single mRNA molecule that codes for several gene products in bacteria
What is an Operator?
A specific region of the DNA near the promoter of a gene, required for the transcriptional control of that promoter
What is an Operon?
A number of adjacent genes transcribed as a polycistrionic mRNA
Expression may be subject to common control mechanism
What is an Operon?
A number of adjacent genes transcribed as a polycistrionic mRNA
Expression may be subject to common control mechanism
What controls the amount of mRNA synthesis?
Repressor proteins synthesised from a regulator gene
What is the function of the Lactose Operon?
Breakdown of disaccharide lactose into the monosaccharides galactose and glucose
What enzyme does the Lactose Operon use to break down lactose?
β-Galactosidase
Which bond does β-Galactosidase cleave?
1-4 bond
Which genes make up the Lac Operon?
- LacZ
- LacY
- LacA
What does the LacI gene produce?
Repressor
Always produced & not part of the Lac Operon
What does the LacI gene produce?
Repressor
Always produced & not part of the Lac Operon
What does the LacZ gene produce?
β-Galactosidase
What does the LacY gene produce?
Permease
What does the LacA gene produce?
Transacetylase
What is the function of Permease?
Brings lactose products into the cell
What is the function of Transacetylase?
Function not known
What happens to the lac operon when there is NO inducer (lactose) present?
- Repressor binds to operator, preventing passage of RNA polymerase.
- No transcription
What happens to the lac operon when the inducer (lactose) IS present?
- Inducer binds to repressor and prevents it from binding to operator
- Transcription takes place
How does the repressor bind to the operator for transcription of the Arg Operon?
Requires a co-repressor (argenine) present
RNA polymerase transcribes Arg Operon while arginine concentrations are low
How does the release of the co-repressor (arginine) affect the Arg Operon?
Blocks transcription of Arg Operon when arginine concentrations are high
How are Inducible operons affected by their gene products?
Switched ON
How are Repressible operons affected by their gene products?
Switched OFF
What type of transcription control mechanism are Induction & Repression?
Negative control
How does Positive Control initiate transcription at the promoter?
An activator protein is required to activate RNA polymerase instead of repressor protein
What operon uses Positive Control to transcribe its genes?
Maltose Operon
Why is an activator protein required in Positive Control for transcription?
RNA polymerase is unable to recognise the target promoter without it
How does a Transcriptional Activator work?
Bends DNA in order to aid the RNA polymerase in recognising the -10 and -35 recognition points on DNA
